1. Field of the Invention
The present invention generally relates to telephone switching methods and telephone switching apparatuses and, more particularly, to a telephone switching method and a telephone switching apparatus which utilizes a general switched telephone network to perform data communication and voice communication.
Recently, an increasing number of subscribers to a general switched telephone network connect a personal computer to a telephone line so as to perform data communication on, for example, the Internet.
Subscribers to the general switched telephone network are given an option of call waiting service in which a sound is produced while a user is engaged in a voice communication so as to indicate that there is an additional incoming call. Upon hearing the sound, the user can selectively communicate with a current partner or a new caller using a hook operation. Recently, the call waiting service has become extensively used.
In the call waiting service, the sound is superimposed on the current telephone line so as to notify the user of a new incoming call. If data communication is performed while the sound is being produced, the sound is superimposed on the data, resulting in damage to the data or an error in communication.
For this reason, the user is required to suspend the call waiting service while he or she is engaged in data communication.
2. Description of the Related Art
FIG. 1 shows an operation performed in the telephone switching method according to the related art.
When subscriber A performs an off-hook operation so as to dial a telephone number of subscriber B, an exchange 110 connects subscriber A to an exchange 120 to which subscriber B belongs. The exchange 120 calls the subscriber B using the telephone number dialed by subscriber A. When subscriber B responds to the call by performing an off-hook operation, subscriber A and subscriber B are connected to each other so that they can start voice communication.
When a call is originated by subscriber C to subscriber A via the exchange 110, an interrupt is asserted to the voice communication between subscriber A and subscriber B in response to the call from subscriber C, if subscriber A subscribers to the call waiting service. A sound is provided to subscriber A indicating that there is a call from another party waiting.
By operating a hook, subscriber A can selectively talk with subscriber B or subscriber C.
A description will now be given of a connection to the Internet.
FIG. 2 shows a connection to the Internet according to the related art.
When subscriber A requests connection to the Internet using a personal computer 200, the personal computer 200 activates a dialer so as to set a telephone line 210 to an off-hook status and dial an Internet service provider 220.
The exchange 110 connects subscriber A to the exchange 120 to which the Internet service provider 220 belongs so that the exchange 120 connects to the Internet service provider 220.
When a call is originated by subscriber C to subscriber A via the exchange 110, an interrupt is asserted to the voice communication between subscriber A and subscriber B in response to the call from subscriber C, if subscriber A subscribes to the call waiting service. A sound is provided to subscriber A indicating that there is a call from another party waiting. Since subscriber A is engaged in data communication using the personal computer 200, the data being exchanged during the communication may be damaged or an error may occur in the communication as a result of the sound being superimposed on the telephone line.
Some approaches to preventing damage to data or an error in communication from occurring as a result of an interrupt during data communication are proposed in Japanese Laid-Open Patent Applications No. 63-142755 and No. 64-71256.
A description will now be given, with reference to FIG. 3, of an approach disclosed in Japanese Laid-Open Patent Application No. 63-142755.
FIG. 3 shows an operation according to Japanese Laid-Open Patent Application No. 63-142755 for preventing damage to data or an error in communication from occurring due to an interrupt to data communication.
Referring to FIG. 3, Japanese Laid-Open Patent Application discloses registering in an exchange 300 a special number (for example, #123) for identifying data communication or facsimile communication. When data communication or facsimile communication is to be performed, subscriber A dials #123 before dialing the telephone number of subscriber B. Upon detecting the special number #123 at the beginning of the number dialed by subscriber A, the exchange 300 disables an interrupt from subscriber C while subscriber A is communicating with subscriber B.
A description will now be given, with reference to FIG. 4, of an approach disclosed in Japanese Laid-Open Patent Application No. 64-71256.
FIG. 4 shows an operation according to Japanese Laid-Open Patent Application No. 64-71256 for preventing damage to data or an error in communication from occurring due to an interrupt to data communication.
Referring to FIG. 4, Japanese Laid-Open Patent Application No. 64-71256 discloses providing in an exchange 400 a registration table 401 for registering telephone numbers of subscribers to whom an interrupt is permitted. By dialing a predetermined special number, a subscriber can make a registration in the registration table 401 (step S3-1).
Assuming that subscriber A is communicating with subscriber B (step S3-2) and there is a request for interrupt from subscriber C to subscriber A (step S3-3), the exchange 400 searches the registration table 401 storing telephone numbers registered by subscriber A in step S3-1 (step S3-4).
If, as a result of the search in step S3-4, the telephone number of subscriber C is found in the registration table 401, the exchange 400 enables the interrupt from subscriber C (step S3-5).
In this way, interrupts from only designated users are enabled.
Japanese Laid-Open Patent Application No. 63-142755 has a drawback in that operability suffers because a subscriber is required to dial a special number before making a call.
Japanese Laid-Open Patent Application No. 64-71256 requires maintaining registration tables for each of the subscribers, resulting in a large number of registration tables. Therefore, the approach disclosed in Japanese Laid-Open Patent Application is difficult to implement in the general switched telephone network. Since an interrupt from non-designated subscribers is enabled during data communication, such approach does not prevent damage to data and an error in communication. Another disadvantage is that the call waiting service is not available for ordinary voice communication for telephone numbers not registered in the registration. The call waiting service such as this lacks availability. Further, subscribers are required to perform a complicated operation in order to provide a registration table.